It is known that use of silicon compounds as the cocatalyst component in a carried-type Ziegler catalyst increases the stereoregularity of the resulting polymer, thus increasing the working characteristics of the polymer.
Such silicon compounds include, for example, diphenyldimethoxysilane compounds (EP45975 (Published Unexamined Japanese Patent Application Nos. 57-63310 and 57-63311), Published Unexamined Japanese Patent Application Nos. 58-138708, 61-296006, WO8805056 (Published Unexamined Japanese Patent Application No. 63-175008), and EP283011 (Published Unexamined Japanese Patent Application No. 63-289004)), diisobutyldimethoxysilane compounds (Published Unexamined Japanese Patent Application No. 62-18406, EP250229 (Published Unexamined Japanese Patent Application No. 63-258907), Published Unexamined Japanese Patent Application No. 2-70708, EP376145 (Published Unexamined Japanese Patent Application No. 2-173010), and Published unexamined Japanese Patent Application No. 3-33103), diisopropyldimethoxysilane compounds (Published Unexamined Japanese Patent Application No. 63-258907, EP350170 (Published Unexamined Japanese Patent Application No. 2-229807), Published Unexamined Japanese Patent Application Nos. 3-33102 and 3-33103), dicyclopentyldimethoxysilane compounds (Published Unexamined Japanese Patent Application No. 2-229807), di-t-butyldimethoxysilane compounds (EP349772 (Published Unexamined Japanese Patent Application No. 2-70708), Published Unexamined Japanese Patent Application Nos. 2-229806 and 3-33102), dicyclohexyldimethoxysilane compounds (Published Unexamined Japanese Patent Application No. 63-258907), cyclohexylmethyldimethoxysilane compounds (Published Unexamined Japanese Patent Application NOS. 2-170803 and 2-229807), cyclohexylethyldimethoxysilane compounds (EP376084 (Published Unexamined Japanese Patent Application No. 2-163104)), t-butylmethyldimethoxysilane compounds (Published Unexamined Japanese Patent Application Nos. 62-11705, 62-20507, 63-92615, and 2-229807), t-butylpropyldimethoxysilane compounds (Published Unexamined Japanese Patent Application Nos. 4-202505 and 5-17319), phenyltriethoxysilane compounds (Published Unexamined Japanese Patent Application No. 57-63311, DE895019 (Published Unexamined Japanese Patent Application No. 58-83006), Published Unexamined Japanese Patent Application Nos. 62-20507 and 61-296006), ethyltriethoxysilane compounds (Published Unexamined Japanese Patent Application No. 57-63310), butyltriethoxysilane compounds (Published Unexamined Japanese Patent Application No. 2-170803), t-butyltrimethoxysilane compounds (Published Unexamined Japanese Patent Application Nos. 62-11705, 63-92615, 63-258907, 3-33106, 3-33105, and 2-70708), t-butyl(t-butoxy)dimethoxysilane compounds (EP419249 (Published Unexamined Japanese Patent Application No. 3-119004)), isobutyltrimethoxysilane compounds (Published Unexamined Japanese Patent Application No. 3-33106), t-butyltriethoxysilane compounds (Published Unexamined Japanese Patent Application No. 2-229807), norbornanetrimethoxysilane compounds (Published Unexamined Japanese Patent Application No. 63-92615) and the like.
However, compounds having benzene rings connected to a silicon atom, such as diphenyldimethoxysilane compounds, will upon decomposition release benzene which is harmful to humans and which remains in the polymers resulting from such compounds. This causes a serious hygienic problem.
While diisopropyldimethoxysilane, dicyclopentyl-dimethoxysilane, dicyclohexyldimethoxysilane, di-t-butyldimethoxysilane, t-butyl(t-butoxy)dimethoxysilane, t-butylmethyldimethoxysilane compounds and the like have aliphatic hydrocarbyl groups on silicon atoms so that there arises no problem from the viewpoint of hygiene but presence of bulky substituents connected to silicon atoms leads to difficulties in their synthesis as well as to high costs.
Diisobutyldimethoxysilane, cyclohexylmethyldimethoxysilane and cyclohexylethyldimethoxysilane compounds can be synthesized by hydrosilylation reaction so that they can be prepared at low costs. However, the stereoregularity itself does not always suffice the requirements for the polymers.
On the other hand, trialkoxysilane compounds, for example, phenyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, t-butyltrimethoxysilane, isobutyltrimethoxysilane, t-butyltriethoxysilane, norbornanetrimethoxysilane and the like, are known to deactivate the activity of catalysts considerably. Hence, in order to prevent the reduction in the activity of catalysts when the trimethoxysilane compounds are used, there have been proposed several technologies which use a dimethoxysilane compound in combination with the trimethoxysilane compounds (Published Unexamined Japanese Patent Application No. 2-70708, 3-33103, 3-33105, and 3-33106). However, each of these causes new problems; for example, they each result in the reduction of stereoregularity and require a plurality of tanks for storing respective silane compounds and feeding them to the plant.
Recently, there have been disclosed methods for preparing low molecular weight polyolefins with trialkoxysilane compounds having a 1-alkylcycloalkyl group (Published Unexamined Japanese Patent Application No. 8-157520 and 8-59730). However, in the case of magnesium chloride-carried catalysts containing trialkoxysilane compounds as a co-catalyst component, it has been difficult to obtain polyolefins having a low molecular weight (MFR&gt;20(g/10 minutes)), a broad molecular weight distribution (MLMFR/MFR&gt;22), and a high stereoregularity, which are suitable for articles obtained by inflation molding or blow molding.
Therefore, an object of the present invention is to solve the above-described problems in preparing polyolefins with a carried-type Ziegler catalyst according to the prior art and provide an olefin polymerization catalyst and a method for the preparation of polyolefins therewith which can, when applied to polymerization of olefins having 3 or more carbon atoms, give, in high yields, highly stereoregular polyolefins having a low molecular weight (MFR&gt;20 (g/10 minutes) and a broad molecular weight distribution (MLMFR/MFR&gt;22).